"Some people are blessed with skin that doesn't damage that way."
Not really. If you are genetically skinny, and if you gain a lot of fat or muscle ... you are bound to get stretch marks.
"And fat = stretch marks is a huge myth."
Well, when I pigged out and got to 260lbs, that's when my stretch marks started.
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JMHO.
I think it has to do with the elasticity of the person's skin. The classis ectomorphs are more prone to stretch marks if they gain a lot of weight than the endomorphs (specially if done fast).
I used to think I never got stretch marks, but that's cause I never really got enough to the point where my skin would stretch. Once I broke the 250lbs mark, I noticed them coming.
This is just my personal experience and from what i've noticed ...
-sk